As if getting enmeshed in a third simultaneous war—with costs soaring in a time of economic peril, yawning budget deficits, and national debt—when no vital national interest was at stake wasn't bad enough, that is not the worst of it.

As in George W. Bush’s invasion of Iraq, analysis of the stated reasons for President Barack Obama’s attack on Libya lead to a lot of head-scratching. Other nations’ leaders have repressed their people more severely than Moammar Gaddafi—for example, 5 million people were slaughtered in the Congo and 2 to 3 million people were killed in Sudan—but the United States did not intervene militarily. In fact, the extent of Gaddafi's repression remains unclear. And contrary to U.S. humanitarian rhetoric, the United States is attempting to help the rebels by decimating Gaddafi’s armed forces. This action probably means that the U.S. just couldn't pass up the chance to take advantage of the revolt in Libya and international support (including from the Arab League) to get rid of an Arab dictator whom it had demonized since the days of Reagan—although for the last few years, the U.S. had kissed and made up with Gaddafi. The U.S. saw this chance slipping away, as Gaddafi’s forces were driving on the rebel stronghold of Benghazi. Also, U.S. “leadership” had been challenged by France, which was chomping at the bit to do in Gaddafi.

Being pushed into an unnecessary and costly war by your allies to regain your leadership is not leadership at all; a true leader would have resisted such inane pressure. And resisting his allies should have been easy for Obama, because the dominant U.S. military brought key combat and support capabilities to the fight that no other country could even come close to matching. Nevertheless, perhaps surprisingly, this is not Obama’s biggest transgression. Obama became so enamored with getting international support, including a U.N. resolution, for his attack that he ignored the U.S. Constitution. And as Congressman Dennis Kucinich, Obama’s fellow Democrat, said, failing to get Congress’s approval for war is an impeachable offense.

In a speech to the nation a week-and-a-half after he initiated the attack, Obama, in an attempt to silence criticism that he had never provided a sufficient rationale to the Congress or the American people for going to war, finally got around to justifying his aggressive actions. Yet going to war without congressional approval is clearly unconstitutional.

People can argue about what the nation’s founders meant on this or that issue, but the first and greatest generation was very clear on this point. One of the founding principles of the country—long lost, especially after the United States became statistically the most aggressive country on the planet after World War II—was anti-militarism. The founders abhorred the monarchs of Europe taking their countries to war for reasons of pride or personal aggrandizement—with the costs in blood and treasure falling on their common subjects. To paraphrase Madison, war is the root of all other forms of government oppression, including exorbitant taxes. To prevent needless wars, one of the most important provisions of the Constitution was that Congress—representing the American people—decided on whether or not to enter war; the executive merely carried out Congress’s will. Even Alexander Hamilton, the most ardent proponent of executive power at the Constitutional Convention, proposed that the Senate “have the sole power of declaring war,” with the executive to “have the direction of war when authorized or begun.” Of course, in the Convention, “the Senate” was modified to the entire Congress, thus upping the standard of approval needed.

James Wilson, the founder most responsible for the text of the Constitution, noted that the provision requiring the Congress to declare war “will not hurry us into war; it is calculated to guard against it. It will not be in the power of a single man, or a single body of men, to involve us in such distress.”

Obama has been careful not to call the air assault on Libya a “war,” maintaining that as commander in chief, he has the authority, without congressional approval, to conduct military operations more limited than war. Yet as Hamilton explained in the 69th Federalist, the founders had a much narrower conception of the president’s role as commander in chief: “[The president’s power of commander-in-chief] would amount to nothing more than the supreme command and direction of the military and naval forces . . . while that of the British king extends to the declaring of war and to the raising and regulating of fleets and armies—all which, by the Constitution under consideration, would appertain to the legislature.”

And the Constitution, with its requirement that Congress grant letters of marque and reprisal and make rules concerning captures on land and water, is quite clear that even limited military actions need to have legislative authorization.

But the presidency has become so imperial that presidents now regularly take the country to war without any congressional declaration of war, and sometimes—as in this case—with no legislative approval at all. Obama is not the first president to ignore one of the central provisions of the Constitution; for major conflicts, Harry Truman was the first transgressor, failing to get a congressional declaration of war in 1950 for the Korean “police action.”

This has been a dangerous precedent for a republic. Congress must end its timidity and insist on exercising its important constitutional check on executive power by passing prior judgment on prospective military actions. And when presidents misbehave, as Obama has, more members of Congress following Kucinich’s courageous implied threat—that is, throwing around the “I” word—might lead to better future executive behavior.

Ivan Eland is Senior Fellow and Director of the Center on Peace & Liberty at The Independent Institute. Dr. Eland is a graduate of Iowa State University and received an M.B.A. in applied economics and Ph.D. in national security policy from George Washington University. He has been Director of Defense Policy Studies at the Cato Institute, and he spent 15 years working for Congress on national security issues, including stints as an investigator for the House Foreign Affairs Committee and Principal Defense Analyst at the Congressional Budget Office. He is author of the booksPartitioning for Peace: An Exit Strategy for Iraq, and Recarving Rushmore.